Face localization detects the locations of predefined detailed facial features and outlines in images. It plays important roles in human face related applications. For example, after faces of different size, shape, pose and expression are aligned, face variations caused by different factors, such as human identity, facial expressions, illumination, etc., can be extracted independently for face recognition, facial expression analysis, and face modeling and synthesis. Face localization is also employed in visual face tracking and model based video coding, in which the face model needs to be aligned with the first video frame so that facial geometry and head pose can be customized. Face localization also plays important roles, for example, in computer vision applications for human-machine interaction. It provides two-dimensional (2D) facial geometry information, which allows face recognition to align faces of different size, shape, pose and expression during training and evaluation stages, so that face variations caused by human identity is modeled better and higher recognition rate can be achieved.
In recent years, some have proposed techniques to do face localization automatically. In other words, the locations of predefined facial features and outlines are automatically detected and returned in an image in which the upright frontal view of a human face in arbitrary scene, under arbitrary illumination, and with typical facial expressions is presented. In one known technique, facial features are extracted using deformable template matching, which models facial features and outlines as parametrized mathematical model (e.g., piecewise parabolic/quadratic template) and tries to minimize some energy function that defines the fitness between the model and the facial outlines in the image with respect to the model parameters. In another known technique, shape statistic model is proposed which models the spatial arrangement of facial features statistically, and is used to localize the facial features from a consternation of facial feature candidates calculated using multi-orientation, multi-scale Gaussian derivative filters.